Can I think myself thin?

David - I'm David Attwell and I work at University College London where my lab studies brain energy use. We're used to the idea of doing exercise to consume energy and reduce body weight, but the brain also uses energy to power our thinking. So, can we use up as much energy by thinking hard as we can by going to the gym? Given the epidemic of obesity in the population, should we be encouraging people to do, let's say, math problems rather than going running?

Information is coded in the brain as electrical signals. These are generated by the entry of positively charged ions, sodium and calcium, into the nerve cells. These ions then need to pumped out of the cells again and it's this pumping that uses most brain energy which is provided as oxygen and glucose in the blood. In fact, when you're sitting quietly, the brain consumes about 20% of the body's energy, say about 20 watts. So, about 20% of the food you eat goes to power your thinking if you do no exercise. Now, if you change what you're thinking about, there are changes of brain energy use, but these are small because some nerve cells increase their signalling while others decrease their signalling. As a result, brain energy use changes by only a few percent, perhaps a few watts. In contrast, when you exercise energetically, the high energy use of muscles can double the body's energy use, increasing it by over 100 watts. So the bottom line is, that the energy use associated with thinking can't be dramatically increased to reduce body weight and there's just no alternative to keeping on doing that physical exercise. Hannah - But is there any other way that we can cleverly use our brains to think ourselves thin? We weigh up the options with Professor of Ingestive Behaviour Marion Hetherington from Leeds University...

Marion - Thoughts can guide behaviour so that you can avoid temptation and so that you can guide your behaviour towards a healthier choice. Dieters often have to amend their behaviour in order to avoid temptation and to resist eating foods which are not permitted. Therefore, thinking yourself thin is not enough. You also have to have cues to remind you to stay on your diet goal. Thinking yourself thin, therefore, is really planning ahead and having a strategy and following it.